1. Field of the Invention
In one of its aspects, the present invention relates to a fluid level control system. In another of its aspects, the present invention relates to fluid treatment system comprising such a fluid level control system. In yet another of its aspects, the present invention relates to a method of controlling the level of a flowing fluid.
2. Description of the Prior Art
Fluid treatment systems are known generally in the art.
For example, U.S. Pat. Nos. 4,482,809, 4,872,980 and 5,006,244 (all in the name of Maarschalkerweerd and all assigned to the assignee of the present invention and hereinafter referred to as the Maarschalkerweerd #1 Patents) all describe gravity fed fluid treatment systems which employ ultraviolet (UV) radiation.
Such systems include an array of UV lamp frames which include several UV lamps, each of which are mounted within sleeves which extend between and are supported by a pair of legs which are attached to a crosspiece. The so-supported sleeves (containing the UV lamps) are immersed in a fluid to be treated which is then irradiated, as required. The amount of radiation to which the fluid is exposed is determined by factors such as the proximity of the fluid to the lamps, the output wattage of the lamps and the fluid flow rate past the lamps. Thus, the UV lamp modules described in the Maarschalkerweerd #1 Patents are typically employed in an open, channel-like system which has a gravity fed flow of water passing therethrough.
U.S. Pat. Nos. 5,418,370, 5,539,210 and 5,590,390 (all in the name of Maarschalkerweerd and all assigned to the assignee of the present invention and hereinafter referred to as the Maarschalkerweerd #2 Patents) describe a fluid treatment system which combines the advantageous features of a closed fluid treatment system in the area where the lamps irradiate the fluid passing thereby by placing a particular architecture in an open channel containing a flow of fluid.
Regardless of whether a fluid treatment system employs the modules taught in the Maarschalkerweerd #1 patents or the architecture taught in the Maarschalkerweerd #2 patents, it is typical to control the level of fluid passing through the open channel by means of a level gate or the like disposed downstream of the fluid treatment device.
Thus, fluid level gates are known generally in the prior art. For background information, see, for example, IRTC Report 01-003 and xe2x80x9cFlap Gate for Automatic Upstream Canal Controlxe2x80x9d, both available from Irrigation Training and Research Center (San Luis Obispo, Calif.).
For example, U.S. Pat. No. 4,606,672 [LeSire] teaches a canal upstream level gate which comprises a gate depending down into a flowing stream from a pivotal access transverse to the stream and an arm extending downstream from the access and gate containing a ballast to force the gate against the flowing stream. The ballast is adjustable along the arm thereby causing the gate to retain an upstream water level as a function of the ballast position therealong. A purported advantage of this device is elimination of trial and error measurements to achieve correct position of the ballast for a desired height of fluid flow upstream of the device.
U.S. Pat. No. 4,877,352 [Tuttle et al. (Tuttle)] teaches a method and an apparatus for control of an upstream water level. The apparatus operates by adjustment of the elevation of a trough assembly of a weir. The weir is slidably mounted in a trough assembly which can be raised or lowered with respect to the flow of fluid. Two vertical screw shafts extend downwardly from a tandem screw jack assembly and are bolted to the trough assembly. The vertical screw shafts raise or lower the trough assembly through rotation of a hand crankxe2x80x94FIG. 3 of Tuttle illustrates this vertical adjustment feature.
U.S. Pat. No. 5,516,230 [Bargeron et al. (Bargeron)] teaches a gate for controlling upstream water level. This gate is purportedly self-actuating and comprises a stepped, radial gate face mounted on a pair of hinge arms extending downstream to a pivot shaft and to a counterweight and support system. The support system for the counterweight includes a pattern of holes and counterweight angle adjustment cams. To adjust the level of fluid upstream of the device, these counterweight angle cams are rotated with a wrench which results in a change to the angle of the risers with respect to the hinge arms connected to the radial gate face. Thus, manual intervention is required to xe2x80x9csetxe2x80x9d the function of this device.
U.S. Pat. No. 6,171,023 [Townshend] teaches a water gate assembly comprising a self-actuating top-hung gate for controlling the flow of fluid in a waterway. The gate is pivotally mounted on a pair of piers located above an upstream section of the gate for allowing the gate to pivot between a closed position and an open position in which water flows beneath the gate. A ballast tank is included in the device and is capable of being charged and discharged via an appropriate inlet and outlet, respectively. In operation, the ballast tank is charged and discharged with water flowing through the waterway.
U.S. Pat. No. 6,193,938 [Wedekamp] teaches a device for treating pre-purified waste water liquid with UV radiation. The device includes an outlet chamber having a weir element which includes a damming wall extending upwardly in the flow of fluid. Several individual weir elements are arranged on the slanted damming wall, the weir elements being formed by upwardly extending tubes. Thus, the flow control system of Wedekamp appears to be a static system in which xe2x80x9cflowing wastewater no longer impacts a vertical damming wallxe2x80x9d.
Thus, it appears that the prior art approach of controlling fluid flow in an open channel is to have a dynamic element which pivots about a single point only (e.g., the approach taught in any one of LeSire, Tuttle, Bargeron and Townshend) or a static system (e.g., Wedekamp).
A problem with conventional dynamic fluid control systems is that they must be adjusted manually to a preset level empirically determined or by calculation of a formula. The problem with the static system of Wedekamp is that it is complicated and costly to construct and must be cast into the open channel through which the fluid flows. Since, in many cases, such open channels are part of an existing fluid treatment plant, the retrofitting cost of adopting the Wedekamp approach is relatively high.
Further, conventional fluid level control systems produce a water level rise as flow increases in order to provide the required discharge. Accordingly, these systems require a relatively large installation footprint which require designers to build channels that are flared or are longer to accommodate these systems at the required flow capacity.
Thus, it would be desirable to have an improved fluid level control system which alleviates one or more of the above-mentioned disadvantages of the prior art.
It is an object of the present invention to obviate or mitigate at least one of the above-mentioned disadvantages of the prior art.
In one of its aspects, the present invention provides fluid level control system comprising:
a gate having a flap portion interconnected to a lever portion, the flap portion being rotatable about a first pivot point, the flap portion comprising a first weight;
a frame fixed with respect to the flap portion; and
a linkage interconnecting the flap portion and the lever portion and being connected to the frame at a second pivot point different than the first pivot point;
wherein the flap portion is rotatable about the first pivot point upon being contacted by the flow of fluid and the linkage is rotatable about the second pivot point to change a closing moment of the gate.
In another of its aspects fluid treatment system comprising:
(i) a fluid treatment zone disposed in an open channel having a flow of fluid therein, and
(ii) fluid level control system comprising:
a gate having a flap portion interconnected to a lever portion, the flap portion being rotatable about a first pivot point, the flap portion comprising a first weight;
a frame fixed with respect to the flap portion; and
a linkage interconnecting the flap portion and the lever portion and being connected to the frame at a second pivot point different than the first pivot point;
wherein the flap portion is rotatable about the first pivot point upon being contacted by the flow of fluid and the linkage is rotatable about the second pivot point to change a closing moment of the gate.
A method for controlling the level of a flow of fluid in a channel at a desired level with a fluid level control system comprising: a gate having a flap portion interconnected to a lever portion, the flap portion being rotatable about a first pivot point, the flap portion comprising a first weight; a frame fixed with respect to the flap portion; and a linkage interconnecting the flap portion and the lever portion and being connected to the frame at a second pivot point different than the first pivot point, the method comprising the steps of:
disposing the flap portion in the channel such that the flow of fluid contacts the flap portion at a first applied force; and
altering a flow condition of the fluid to cause the flow of fluid to contact the flap portion at a second applied force different than the first applied force to cause relative movement between the flap portion and the lever portion.
In another of its aspects, the present invention provides a fluid level control system comprising: a gate having a flap portion connected to a linkage which is adjustable with respect to the flap portion; wherein the flap portion is movable upon being contacted by an applied force thereby causing movement of the linkage to cause adjustment of a closing moment of the gate and control of the rate of change of an upstream level of a fluid flow through the system, the flap portion comprising a first weight.
Thus, the present inventors have conceived of a novel approach to the design a of fluid level control system. This novel approach is a significant deviation from prior art approaches. Generally, in the present fluid level control system, as a flow of fluid at a steady state flow condition changes (i.e., steady state flow condition becomes a transient flow condition), the resulting change to the applied force on the gate of the present fluid level control system results in relative movement between the lever portion and the flap portion. In contrast, the prior art approach has been to fix the flap portion with respect to the gate so that, under a similar transient flow condition, the flap portion and the lever portion move as a unit and there is no relative movement between the two. In the preferred embodiment, the approach involves the flow of fluid to actuate the flap portion to rotate about a first pivot point which serves to actuate the linkage to rotate about a second pivot point independent of the first pivot point. This results in a fluid level control system having a number of advantages.
Conventional weirs, gates and other fluid level control devices have been used to maintain upstream water depth within a desired elevation range. However, most open channel level control devices produce a water level rise (increase in head) as flow increases in order to provide the required discharge. Such control devices typically have large installation footprints, which force designers to build channels that must be flared or are extra long to accommodate the devices at the required flow capacity. The present fluid level control system obviates the requirement to modify the channel; the only condition being substantially free discharge (i.e., substantially no backwater pressure) downstream of the gate. The present fluid level control system may be installed directly into a prismatic channel with a footprint approximately equal to the cross-section of the channel.
In a preferred embodiment, the present fluid level control system will accurately control upstream depth of water in the channel without incurring additional head (increase in water elevation) up to an inlet flow velocity of 1.3 m/sec or more. In the preferred embodiments of the present fluid level control system, this control is achieved on-line and in situ (i.e., continuous self-adjustment of the system without the requirement for manual intervention).